A vibration absorber valve of this kind is known, for example, from the German patent specification No. 37 12 477. The particular feature of the prior-art vibration absorber valve consists in that at least a part of the front surface of its valve body and valve seat are disposed at a distance from each other (the ratio of the pressurized front surface relative to the rear pressurized front surface being 0.5-1 and the ratio of a pressurized annular surface relative to the rear pressurized front surface being 0-0.5). This design provides for an optionally adjustable vibration absorption in the traction stage and in the thrust stage. This function is made possible primarily due to the hydraulically pressurized functional surfaces of the valve body, the switching behavior of the armature design and the use of a solenoid which forms the electro-mechanical transducer.
The above referenced vibration absorber valve has the disadvantage that the (particularly in the range of low volumetric flow rates which pass through the vibration absorber valve) no restricting function can be attained independent of the absorber pressure. In the range of the pressure-dependent restricting function the above referenced vibration absorber valve represents a control loop which determines its dynamic behavior, so that a controllable vibration absorber equipped with such an absorber valve is less adapted for use in a semiactive chassis regulating system. A further advantage is seen in the fact that the family of characteristics of a vibration absorber of this kind is fixed by the dimensioning of the component parts of the vibration absorber valve and cannot, for example, be modified during driving in the event of an adaptive chassis control action.
It is, therefore, the object of the present invention to propose a vibration absorber valve of the kind which the influence the absorber pressure has on the restricting function in the range of low volumetric flow rates is minimized. Simultaneously the dynamic behavior in the chassis regulating process is to be improved. A further object is provide a vibration absorber valve that can be electrically altered to provide a family of response characteristics.
According to the invention, this object is attained in that the valve body is directly coupled to a measuring apparatus which monitors the actuating travel of the valve body and whose output signal is conveyed to an electric circuit which actuates the electromechanical transducer in such a way that in a first range of volumetric flow rate a restricting function and in a second range of volumetric flow rate a pressure-limiting function are performed.
As to process, the solution of the forementioned object consists in that the output signals of the regulator are conveyed, on one hand, to a comparator circuit Jointly with output signals of the measuring apparatus monitoring the actuating travel of the valve body and, on the other hand, to a first amplifier, within said comparator circuit a differential value being formed which is transmitted to a second amplifier, and in that the output signals of the two amplifiers are conveyed to a variable delimiter which limits the output signals of the second amplifier depending on the output signals of the first amplifier and conveys them to the electrical output stage of the vibration absorber valve.
In an advantageous further development a further improvement of the dynamic behavior of the inventive vibration absorber valve is attained in that the electromechanical transducer is configurated in the shape of a plunger coil which interacts with a permanent magnet and whose carrier forms the valve body.
Favorable conditions for a balancing of forces of flow occurring within the absorber valve and a coupling of the electromechanical transducer are created in a further development of the subject matter of the invention in that the valve body is configurated in the shape of a bushing which is slidingly guided on a cylindrical guide element and which interacts with cross-sectional areas of flow being provided in said guide element.
In this conjunction, it will be of particular advantage in the interest of a smooth functioning of the inventive vibration absorber valve, respectively of a vibration absorber equipped with it, if and when during the interaction of the valve body with said cross-sectional areas of flow a balancing of the hydraulic forces takes place which occur in the range of action. This provision affords, in addition, a reduction of the energy requirements of the electromechanical transducer.
In another advantageous development of the inventive thought the balancing of the forces of flow mentioned before is, for example, achieved in that the valve body and/or the chamber disposed downstream of the cross-sectional areas of flow as seen in the flow direction are configurated such that a deviation of the volumetric flow is ensured. In this configuration, the front surface of the bushing-shaped valve body has preferably the shape of a truncated cone.
According to a further inventive feature another possibility to counteract the forces of flow consists in that said cross-sectional areas of flow end up in an annular hydraulic chamber which is connected to the outlet of the valve arrangement in such a manner that the static pressure coming about in said annular chamber lets become effective a hydraulic force component which counteracts Bernouille forces acting on the valve body.
It will also be of advantage when radial pressure-relieving grooves are envisaged in the guide element which end up in a slot being configurated between the valve body and the guide element. By this measure the effect of the hydraulic clamping is prevented in this range.
In this context, said guide element is preferably furnished with pressure agent ducts which are linked to the slot and which are preceded by a filter element. As a result of this, a smooth supply of the slot with filtered oil is safeguarded, so that the risk of soiling is largely eliminated.
In a further design version of the invention, the risk of soiling of the inventive absorber valve is reduced in that an annular groove is provided in the range of the cross-sectional areas of flow. Only a short sealing slot with a slight pressure differential is disposed between the cross-sectional areas of flow and the annular slot, as a result whereof contaminants are impeded from entering into the slot.
In order to ensure that no pressure balance takes place at the valve body during operation, it is a bore is provided within the guide element. A cylindrical element is guided within the bore and is loosely axially abutted against the valve body.
In order to make sure that the function of the vibration absorber equipped with the inventive absorber valve is preserved even in the event of a failure of the electromechanical transducer (so-called fail-safe function), it is envisaged in a preferred embodiment of the subject matter of the invention that the valve body is suspended on a bending spring which is clamped in the valve housing. This provision is expedient in particular In conjunction with bidirectional transducers. The bending spring may, for example, be configurated as a spring plate which is furnished with passages. Furthermore, the bending spring can support the valve body, independently of the electro-mechanical transducer in order to further minimize the frictional effects.
A design version of the invention which is less expensive to manufacture and which reduces the space requirements. This design is distinguished by the measuring apparatus monitoring changes of magnetic variables which are caused by the adjustment of the valve body.
In this configuration, the measuring apparatus may preferably be formed by a permanent magnet being fixed to the valve body, respectively to an element coupled to it, and by a sensor element recording the changes of its magnetic field.
It is envisaged according to another advantageous further development of the subject matter of the invention (which is especially adapted for application at more elevated temperatures) that the sensor element is formed by a magneto-resistive element. However, said sensor element may also be formed from a Hall element.
A measuring apparatus working reliably, independent of the influence of external magnetic fields is constituted, for example, by a reflecting light barrier.
A sturdy measuring apparatus being insensitive to soiling may be configurated in the shape of an arrangement working by the eddy current principle.
In the realization of the inventive process for the continuous adjustment of the vibration absorbing force of a vibration absorber being equipped with the absorber valve according to the invention it is of particular advantage that for chassis regulation purposes the pressure (p) adjusted within the vibration absorber allows, in the static condition, to be determined from the sensor signals and control signals through the following equation: ##EQU1## since the forces of flow are balanced. In the equation: K.sub.mag is the proportional control factor of the electromechanical transducer,
i is the current being supplied to the plunger coil, PA1 C is the spring rate of the bending spring, PA1 y is the actuating travel of the valve body, and PA1 A.sub.1 is the area of the cylindrical element which is abutted with the valve body.
Further details, features and advantages of the invention will be revealed by the undermentioned description of one embodiment, making reference to the accompanying drawing.